Add a new `File.stat(path)` static method that returns a `Stat` object with low-level file system metadata for both files and directories. Include a test file `stat_static_directory.wren` that validates the returned `Stat` object's type and field types (device, inode, mode, linkCount, user, group, specialDevice, size, blockSize, blockCount) against a known test directory.
Extend File.readBytes with a second overload accepting an offset argument, allowing reads to start at any byte position from the beginning of the file. The existing single-argument variant now delegates to the new two-argument version with offset 0. Validation for the offset parameter mirrors the existing count checks, aborting on non-numeric, non-integer, or negative values. The underlying C implementation passes the offset directly to uv_fs_read, replacing the previous hardcoded zero. Documentation in the io module markdown is updated with usage examples for both signatures, and the old TODO comment about missing offset support is removed. New test files cover offset-based reads, edge cases (zero offset, past-end offset, zero count with offset), and error conditions for invalid offset arguments.
Restructure the documentation hierarchy to prepare for documenting additional built-in modules. Move all core library documentation from `doc/site/core/` to `doc/site/modules/core/`, rename `modules.markdown` to `modularity.markdown`, remove `^category` metadata lines from all affected pages, update cross-reference links to use relative paths under the new structure, and add a TODO placeholder to the Class class page.
